How much does colder weather increase power?
Thread Starter
Pro
Joined: Apr 2007
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From: Arvada CO
How much does colder weather increase power?
Here in Denver yesterday when I left for work it was just over 50 degrees. With my mods my LS-2 is 400rwhp/400rwtq. When I drove home, a cold front moved in and the outside temp was 25 degrees. To me the car was very different than the drive to work. Without a doubt, I felt more sotp pull. Just made me smile. 
Am I imagining this or is there that much of a power difference with a big temperature drop? How much power increase would there be?
Am I imagining this or is there that much of a power difference with a big temperature drop? How much power increase would there be?
Thread Starter
Pro
Joined: Apr 2007
Posts: 663
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From: Arvada CO
542rwhp!! Outstanding. I'm thinking you need to be careful on warm days as well.
My new Firestone wide ovals seemed to be OK yesterday for the first test run below freezing. You are right though, I remember how much the traction changed on my Goodyear runflats when it dropped below freezing.
Race Director
Joined: Mar 2005
Posts: 10,399
Likes: 25
From: Austin Texas
The ECM is programmed for major timing changes from temps. The intake air temp and the coolant temp both affect ignition timing. I've seen statements on this Forum of 3 HP per degree of timing. Add in high barometric pressure and dry air and there is a very noticeable increase in RWHP.
Keep in mind that cooler temps also have an effect on traction, cold tires and cold pavement = tire smoke.
Keep in mind that cooler temps also have an effect on traction, cold tires and cold pavement = tire smoke.
Le Mans Master
Joined: Aug 2008
Posts: 5,578
Likes: 61
From: Austin TX
Figure about 3% change in power for every 1000 ft change in density altitude.
When you left for work, the DA was about 5800 feet.
Later the DA dropped to 3700 ft due to the temp drop and increase in baro pressure.
So, you enjoyed an increase in power of 6%, or about 24 rwhp. Something you'd definitely feel.
When you left for work, the DA was about 5800 feet.
Later the DA dropped to 3700 ft due to the temp drop and increase in baro pressure.
So, you enjoyed an increase in power of 6%, or about 24 rwhp. Something you'd definitely feel.
Instructor
Joined: Dec 2007
Posts: 115
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Humidity also has a big impact. You dont want water taking up room in your air. The more water in the air effects the way the flame burns and has a slight affect on dynamic timing, even though your spark starts at the same time.
Its because you have to vaporize the water before the gass burns, taking longer for the combustion process to finish the burn.
Its because you have to vaporize the water before the gass burns, taking longer for the combustion process to finish the burn.
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Thread Starter
Pro
Joined: Apr 2007
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From: Arvada CO
Figure about 3% change in power for every 1000 ft change in density altitude.
When you left for work, the DA was about 5800 feet.
Later the DA dropped to 3700 ft due to the temp drop and increase in baro pressure.
So, you enjoyed an increase in power of 6%, or about 24 rwhp. Something you'd definitely feel.
When you left for work, the DA was about 5800 feet.
Later the DA dropped to 3700 ft due to the temp drop and increase in baro pressure.
So, you enjoyed an increase in power of 6%, or about 24 rwhp. Something you'd definitely feel.
I can't imagine what this car would feel like at sea level with cold temps.
Melting Slicks
Joined: Apr 2007
Posts: 3,290
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From: Willow Springs IL
Colder air is denser. This allows more air to enter the combustion chamber per power stroke which makes more power. An intercooler does the same thing on a subercharged car. My A&A car makes 567rwhp (this was done in the summer) and definately feels more powerful in cooler weather. Part of the SOTP feeling may just be that it doesn't hook up as well which makes it feel faster because it's spinning the tires alot more.
Race Director
Joined: Oct 1999
Posts: 13,298
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From: Somers NY
I cant give you any HP improvements, but I can give you MPH & ET in the 1/4 mile at various temps... with the "EXACT" same car and set up.
In cool weather 45 deg. my car ran 12.08 @ 115 mph..(corrected alt. was 400')
same car in 83 deg. 12.47 @ 111 mph...(corrected alt was 2700')
In cool weather 45 deg. my car ran 12.08 @ 115 mph..(corrected alt. was 400')
same car in 83 deg. 12.47 @ 111 mph...(corrected alt was 2700')
Last edited by jpee; Oct 10, 2009 at 12:49 PM.
Pro
Joined: Sep 2009
Posts: 536
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From: Los Angeles California
To the best of my knowledge the four factors usually considered in air density, and their effects on power are:
1. elevation: +/- 3% per 1000 feet (as stated above)
2. temperature: +/- 2% per 10 degrees F (15 degrees = 1000 ft of DA)
3. daily barometric pressure changes independent of elev/temp: every +/- 1% changes power by +/- 1%... but daily variations rarely exceed 1 percent.
4. humidity: a 10% change to humidity has an effect equiv. to 50ft of elevation change.
So, elevation and temp are the dominant factors. The "correction tables" I have seen show about 1.3% change to e.t. and mph for every 1000 ft of DA.
1. elevation: +/- 3% per 1000 feet (as stated above)
2. temperature: +/- 2% per 10 degrees F (15 degrees = 1000 ft of DA)
3. daily barometric pressure changes independent of elev/temp: every +/- 1% changes power by +/- 1%... but daily variations rarely exceed 1 percent.
4. humidity: a 10% change to humidity has an effect equiv. to 50ft of elevation change.
So, elevation and temp are the dominant factors. The "correction tables" I have seen show about 1.3% change to e.t. and mph for every 1000 ft of DA.
Instructor
Joined: Jan 2005
Posts: 131
Likes: 0
From: Tyler TX
Looked at the weather in Denver yesterday: Temp 22; relative humidity 80%; barometric pressure 30.23.
If corrected from a standard 400 hp you would have 352 hp.
Today numbers were 37;57;29.87. If temp were 55 deg with other variables the same, you would see only 331 hp -- a 21 hp loss.
If corrected from a standard 400 hp you would have 352 hp.
Today numbers were 37;57;29.87. If temp were 55 deg with other variables the same, you would see only 331 hp -- a 21 hp loss.
